A large-scale study found that a stretch of the genetic material DNA is damaged in the chromosome of people with the conditions.
Autism and schizophrenia are already known to be influenced by genetic factors and experts have been looking at rare copy number variations (CNVs) – insertions or deletions of genomic material.
While it is known these variations play a common role in the two disorders, this is the first time a specific CNV which confers very high risk has been identified.
The research, led by experts at Emory University in Atlanta in the US, was published in the American Journal of Human Genetics.
Experts analysed the DNA of more than 23,000 patients with autism, developmental delay, intellectual disability or schizophrenia. =
They detected a recurrent deletion on a region of chromosome 17 in 24 of these patients.
No such deletion was detected in any of the more than 52,000 healthy people acting as controls.
One of the authors on the study, Dr David Ledbetter, said someone with this deletion was almost 14 times more likely to develop autism or schizophrenia than a person without it.
The deleted 17q12 region of the chromosome contains 15 genes, including one called HNF1B.
This gene has already been linked to a condition called renal cysts and diabetes syndrome (RCAD), whose sufferers often have neurodevelopmental disorders.
Around one in 110 people are thought to be affected by Autism Spectrum Disorder (ASD), which covers a range of related conditions.
All are characterised by difficulties in social interaction, communication and understanding other people’s emotions and behaviour, but severity can vary widely.
An estimated 133,500 children and young people under the age of 18 in the UK suffer from autism.
Lead author, Dr Daniel Moreno-De-Luca, said: ”We have uncovered a copy number variation that confers a very high risk for ASD, schizophrenia, and neurodevelopmental disorders.
”This is significant, because the 17q12 deletion is among the 10 most frequent pathogenic recurrent genomic deletions identified in children with unexplained neurodevelopment impairments.
”We believe it also may increase risk for other psychiatric conditions such as bipolar disorder.”
In June, a landmark study into the causes of autism identified key genetic fingerprints that could help doctors diagnose the disorder in children.
The research, conducted by around 60 teams of experts from 12 countries including the UK and Republic of Ireland, identified CNVs that were almost 20% more common in autistic children than in unaffected individuals.
Many of the CNVs in the study occurred in regions of the genetic code already implicated in autism while others were found in previously unsuspected regions.
Telegraph Uk